When light from an object in the field of view of a human subject's eye enters the eye through the pupil, the light is focused by refraction through the optical system of the eye onto the retina, forming an image of the object on the retina. Photoreceptor cells in the retina react to the light and send signals through the optic nerve to the brain, where the signals are perceived as the object in the visual field. The photoreceptor cells are not uniformly distributed on the retina, and the resolution of the perceived object is determined in part by the density of the photoreceptors at the location on the retina where the image of that object is formed. The resolution of the perceived object is also determined in part by how correctly the image is focused on the retina by the eye's optical system. The eye's refracting optical elements include the cornea and the lens. If those elements are not able to focus on the retina, the image formed will be distorted and the subject's vision will not be optimal.
The photoreceptor cells in the retina that detect light are called rods and cones. The cone cells, named for their conical shape, function best in relatively bright light and are responsible for detecting color. The cones are most densely packed near a point on the retina called the fovea, and become less dense moving away from the fovea. The fovea is a small pit-like structure disposed near the central axis of the optics of the eye. Thus, the cones are responsible for high resolution vision of well-lit objects in the center of the visual field. In contrast, the rod cells, named for their cylindrical shape, function well in dim light and are most densely concentrated at the periphery of the retina, becoming less dense moving toward the fovea. The rods thus provide for peripheral vision and night vision.
In a healthy eye, light from the center of the field of view enters the pupil and is sharply focused near the fovea, whereas light from the periphery of the field of view is focused at corresponding points on the periphery of the retina. However, any of a plurality of disorders can cause the optics of the eye to focus light improperly on the retina, causing the subject's vision to be blurred.
To resolve some disorders, such as clouding that develops in the eye lens (called a “cataract”), the natural lens may be surgically removed, and an intraocular lens (IOL) surgically implanted in the eye, typically placed at the former location of the natural lens of the eye.
IOLs are designed to work in conjunction with the optical elements of the eye (e.g., the cornea) to produce a sharp image only at the on-axis focal point on the retina and the paraxial region centered thereon. In general, no consideration is given to the off-axis optical properties of the retina or the optical system. Accordingly, even when a subject's vision is corrected at the center of the visual field, the peripheral image in general remains out of focus, resulting in a retinal image that is not optimal. As such, the subject's corrected vision is not as good as it could be, and peripheral vision and night vision are generally much worse than optimal.
Moreover, prior art IOLs do not correct any form of central vision loss, because the only portion of the retinal image that is in focus is located at the point where central vision occurs, i.e., where the central axis of the optics of the eye intersects the retina. In addition, some disorders involve changes in the retinal surface topography, such as substance buildup in the outer retina. Because prior art IOLs only focus light near the fovea, they do not correct for such changes in the diseased peripheral retinal surface.